1. Field of the Invention
The present invention relates generally to an improved data access module for use in 3.5", 2.5" and smaller rigid or hard disc drives. More particularly, the invention relates to a combination stand alone data access module having magnetoresistive rotary position indicating means and an improved magnetic head and slider assembly which exhibits improved air bearing characteristics.
2. Brief Description of the Prior Art
Computer hard disc drives having high data storage capability in excess of five megabytes and which exhibit rapid and accurate data access times are well known in the art. The known disc drive mechanisms typically comprise a data access module having multiple read/write heads, which are positionable relative to the discs via an arm assembly, and a voice coil actuator which is part of the arm stack assembly or disc drive. Current state of the art disc drive and data access modules having high memory storage capability and performance are limited principally to high end machines such as large IBM mainframes and the like.
In the area of personal computers, especially portable computers such as laptops, notebooks and the like, a major objective is the realization of a small disc drive which offers maximum memory storage capability, fast and reliable data access, and which is capable of running for extended time periods on battery power alone. In typical hard disc drives, a transducer is mounted on a ceramic slider assembly and is commonly referred to as a magnetic head. The magnetic head is positioned over the recording media (typically a rotatable magnetic disc) such that it floats on a cushion of air or "flies" over the magnetic storage media and transmits signal responses back and forth between the computer and the disc. The magnetic head is mounted on a flexure or suspension assembly which, in turn, is mounted to an arm assembly. The arm assembly includes an actuator, typically a voice coil, by which the trajectory of the arm, and hence the positioning of the magnetic head with respect to a desired data track on the disc, is controlled.
The early arm assemblies positioned the magnetic head in a linear fashion and are commonly known in the art as linear positioning devices or linear actuators. An example linear actuator is disclosed in U.S. Pat. No. 4,359,762 issued to Stollorz. A major disadvantage with linear actuators is that they are expensive to manufacture and they do not lend themselves to miniaturization and high capacity drives since their stepper motors are not capable of incremented movement of about 700-800 tracks per inch (TPI). Other disadvantages associated with linear positioning devices include the related problems of excess signal noise and large power usage. These problems are due primarily to the fact that the signal path between the transducer head and the signal processing circuitry in the disc drive is unduly long. Thus, additional filter and amplification electronics are necessary to overcome these problems.
An alternative approach to positioning the transducer head on the disc is by use of a rotary actuator. This was an early attempt to achieve a miniaturized actuator assembly. Rotary actuators typically have significantly shorter length arm assemblies than a linear actuator since the pivot of the rotary actuator can be mounted immediately adjacent the outer radial edge of the rotatable disc. In this manner, the transducer head sweeps through an arcuate angle, typically 15 to 30 degrees, while accessing different data tracks on the disc. An example of a rotary actuator implemented a removable cartridge for use in high density disc drives is shown in U.S. Pat. No. 4,965,691 issued to Iftikar et al. In this device, and as is typical with current commercial rotary actuator disc drives, the read/write circuitry for the magnetic head is separate from the positioning arm and is disposed in the removable cartridge.
Even though the signal path distance between the transducer head and the data processing electronics in this device is reduced, there still remain problems of excess signal noise and high power usage since in view of directing the signals off the rotary arm assembly for processing by the appropriate circuitry in the cartridge and/or computer. Further, rotary access introduces new problems associated with maintaining a constant flying height and stability for the slider assembly since it now moves at a changing angle with respect to the spinning disc as it accesses different data tracks. This angular relationship between the longitudinal axis of the slider assembly and the direction of spinning movement of the magnetic disc is known in the art as "skew angle".
When the slider assembly is positioned over a moving disc, air is introduced at the forward or leading slider edge, pressurized, thus forming an air bearing under the slider. As the rotary access slider changes position across the moving disc from one data track to another, changes in the tangential disc velocity and skew angle of the slider affect the air bearing pressure under the slider assembly. These variables cause the slider to roll in one direction or another or fly at different heights. It is desirable to control the flying height since this affects the reliable data transfer between the transducer and the recording medium. These problems are exasperated when a miniaturized data access module is contemplated since design tolerances associated with the positioning arm, flexure and their physical connections are greatly magnified and detract from the efficiency and accuracy of the transducer.
U.S. Pat. No. 4,673,996 issued to Dr. James W. White teaches to provide transverse pressurization contours (TPCs) along the outer and inner longitudinal side edges of the slider rails of a slider suspension assembly in an effort to overcome the problems of roll and to help the slider in maintaining an even flying height as it moves across a spinning disc with a changing skew angle. The transverse pressurization contours provide a pressurization region along a leading side edge of each slider rail and a depressurization region across the opposite trailing side edge of each slider rail so that a substantially symmetrical pressure profile across the air bearing is achieved.
In U.S. Pat. No. 4,870,519 also issued to Dr. White, an improvement to the transverse pressurization contour concept is disclosed. In this patent it is recognized that the damping ability of a two rail slider assembly is enhanced by selectively tailoring the configuration of each transverse pressurization contour along the side edges of the slider rails for a particular disc drive application since the effectiveness of the transverse pressurization contours depend upon the specific disc radius, disc rpm, and range of skew angle magnitudes that are present in the data access module system.
In U.S. Pat. No. 4,218,715 issued to M. F. Garnier, a two rail slider assembly is disclosed wherein each slider rail is provided with a shallow recess or relief portion such that an ambient or slightly subambient pressure is produced in these regions during flying operation of the slider head assembly. These relief portions are alleged to provide the slider with mechanical stability with little or reduced sensitivity to skew and discurvature or ripple of the disc while preserving high air bearing stiffness.
Although the prior art has proposed slider rail configurations which address the problems of roll and uneven flying heights, the prior art does not adequately address the problem of generating a sufficient air bearing stiffness at the trailing edge of the slider assembly such that the transducer head is maintained at a low flying height with sufficient air bearing stiffness. Air bearing stiffness and dampening are of particular importance when the data access module is to be used in a disc drive of a portable computer such as a laptop, notebook or the like, wherein the likelihood of shock and other damaging vibrational movements during use are common. Inadequate air bearing stiffness in these drives will permit the transducer head to "crash" or contact the recording media, thus resulting in premature wear and unreliability of the magnetic head assembly.
Accordingly there is a definite need in the art for an improved data access module wherein the head assembly exhibits improved air bearing stiffness and dampening qualities. There is also a need for improved data access module which may be assembled in miniaturized form for use in 3.5", 2.5" and smaller disc drives and wherein the signal path distance between the transducer head and the data processing electronics is greatly reduced so that the problems of capacitance loading and excess power usage are overcome.